Method for recovering pyridine



April 14, 1942. WALD ET AL 2,279,585

' METHOD FOR REGOVERING PYRIDINE Filed Nov. 8, 1939 INVENTORS MAX D.WALD & 'FP/WKA KA/e/vAT Z.

ATTORNEYS.

Patented Apr. 14, 1942 UNITED STATES PATENT OFFICE METHOD Fon nncovnnmerrnmmn Max D. Wald, University Heights, Ohio, and

Frank A. Karnatz, Indianapolis, Ind., assignors, by direct and mesneassignments, to Republic Steel Corporation, Cleveland, Ohio, acorporation or New Jersey Application November 8, 1999, Serial N6.303,396 3 Claims. (01. 260-290) This invention relates to a new andimproved method for recovering pyridine economically and efficientlyfrom coke oven gases.

Altho it has long been known that pyridine is present in gases which areformed when coal is being cokecl, the only method proposed, so far as weare aware, for recovery of pyridine from such gases is the so-calledbatch process, and it g has been used little, if at all, in thecomm'ercia production of pyridine. This batch process consisted brieflyof passing coke oven gases thru a saturator containing dilute sulphuricacid until the solution was substantially saturated with pyridine, thatis, until the pyridine content was approximately 5%. Then the saturatorwas out out of the line and emptied and the liquid was treated withammonia 'to spring or release the pyridine which then rose to thesurface and could be separated from the other liquid and therebyrecovered.

There were certain outstanding objections and disadvantages inherent inthis batch process. A' considerable amount of equipment was requiredwhich not only would occupy space that might be at a premium at the cokeplant but which would be expensive to install and to maintain. Forexample, storage tanks for the saturator solution and for thepyridine-free solution are necessary. The saturator in operation must betaken out of service so that the acid bath can' be removed, and a sparesaturator must always be available and ready for operation.

Another disadvantage was that the recovery of pyridine was inefficientor quite expensive. Since the sulphuric acid solution would ratherquickly lose its power to absorb pyridine, the solution had to bewithdrawn from the saturators at comparatively short intervals to avoidthe loss ofv pyridine in the gases leaving the saturators and in theammonium sulphate removed. The pyridine in the saturator bath goes tocontaminate the ammonium sulphate and is lost. If, in order to avoid theloss of pyridine either in the gases leaving the saturator or in theprecipitated ammonium sulphate, the saturator solution were -expensivein operation. The present method avoids the objections and disadvantagesof the batch" process and has been found, in commercial operation, to behighly efficient and yet inexpensive.

The present invention may be briefly described as follows:

Coke oven gases, which have been freed from tar and other substances inthe ordinary wellknown manner but which contain ammonia and pyridine,are passed through a solution of dilute sulphuric acid wherein theammonia and pyridine contents of the gases are absorbed. The solutioncontaining ammonium sulphate and pyridine and its'compounds is,preferably continuously, removed from the saturator and treated withammonia gas derived from the distillation of the ammonia liquor obtainedin the coking process. This treatment liberates, the pyridine, thelatter being separated and recov ered whilethe solution from-which thepyridine has been removed is returned to the saturator. The free acidcontent of the solution in the saturator is maintained substantiallyconstant, as is conveniently done by adding fresh sulphuric acidcontinuously or periodically to the solution in the saturator tocompensate for the acidwhich has been neutralized by ammonia in theformation of ammonium sulphate. The precipitated ammonium sulphate maybe removed from the saturator periodically, The pyridine content of thesaturator solution is maintained below aboutv 3% and preferably belowabout 2%, as may be done by withdrawing the solution from the saturatorat a suitable rate.

The present method difiers from the "batch" process in such importantparticulars as the maintenance of a substantially constant ,freesulphuric acid content in the solution in the saturator; the preventionof the pyridine content from exceeding the point where losses ofpyridine begin to occur either in the outgoing gases or in contaminationof the precipitated ammonium As shown by the drawing accompanying andforming a part of this application, the apparatus comprises a saturatorI into which coke oven gases may enter thru main 2 and from 'thesaturator may be discharged for separation from the saturator solution.The precipitated ammonium sulphate with some solution may beconveniently removed onto the drain tables by use of an ejector 5 whichconsists of two concentric tubes extending from above the drain tableoutside of the saturator to a point within the precipitate in thesaturator, the inner tube being attached to a source of compressed air(not shown) and the upper end of the outer tube being connected todischarge onto the drain tables. The liquid which drains Ofl from theprecipitate returns to the saturator thru pipe line 4a and the ammoniumsulphate is dried by means of centrifugal dryers and is then readyforsale.

Each saturator l is connected from a point well below the surface of theliquid contained therein to a reservoir 6 known as a lye pot. Theconstruction and arrangement of this so-called lye pot and the pipesleading to and from it are such that certain operations are inherent inits use. This apparatus operates to show the level of liquid in thesaturator because of the open connection between the pot and thesaturator. This apparatus also inherently operates to reduce the amountof ammonium sulfate in the liquid, passing into pipe 1 as compared withthe amount in the liquid in the saturator. The sulfate so removedconsists of sulfate in suspension as well as sulfate in solution in theliquid in the saturator.

When the present process is operating, sulfate in suspension is settlingtoward the bottom of the saturator under the force of gravity. Since theinlet pipe to the lye pot extends upwardly from a substantiallyhorizontal open end such settling sulfate will tend to continue on pastthe open end of the inlet pipe and will not tend to flow up thru thatpipe with outgoing liquid. A similar action takes place in the lye potitself. As a result the amount of sulfate in suspension in the liquidentering pipe I is less than in the liquid in the saturator and thedecrease is inherent in the normal operation of the apparat lusincluding the pot 6, its intake pipe, and P D The-normal inherentoperation of the lye pot and its intake pipe is to tend to cool theliquid passing therethru. This cooling action is the result of theexposure of these parts to the atmosphere as appears in the drawing andthe lack of application of external heat to these parts.

' In view of the exposure of the lye pot to the air and the slowmovement of liquid through it substantial cooling action is inherent andimevitable. Thus saturator liquid heated by the entering gases tends tocool in passing thru these parts. Since the solubility of ammoniumsulfate decreases with temperature decreases, sulfate which was insolution tends to precipitate out in solid form as the temperature ofthe liquid decreases and such sulfate is collected in solid form in thelye pot 6. A pipe I, which has an inlet end below the surface ofsolution in the reservoir, leads to a centrifugal pump 8 which is drivenby motor 9 which withdraws the saturator solution from the reservoir andpumps it into the pipe line H) which empties into a treating orneutralizing tank II. The tank H is preferably provided with a slopingbottom and an outlet near the lower end thereof which opens into aseparating tank I2. A line l3 which is connected to a source of ammoniavapor enters the top of tank II and discharges ammonia into the lowerportions of the pyridine-containing may be pumped by centrifugal pump I6actuated by motor I I thru line l8 to the drain tables '4 of thesaturator and returned thru pipes 4a into the saturators.

.Such gases as enter tank H with the ammonia vapor and are not'absorbedby the liquid, for example, carbon dioxide and hydrogen sulphide, passinto tank I2 and escape therefrom through vent i9.

Fresh sulphuric acid may be added to the solution in the saturatorsperiodically or continuously by being delivered onto the drain tables orpumped into the saturator thru a line (not shown). I When the presentmethod is to be initiated, one or more saturators are supplied with asuitable quantity of water containing between about 6% and about 8% ofsulphuric acid. In the apparatus shown on the accompanying drawing eachsaturator contains about 4,000 gallons of such a. solution. Commercial,77%, 60 B. sulphuric acid may be used.

Coke oven gases from which ingredients named above have been removed butcontaining ammonia and pyridine bases, are then passed thru mains 2continuously into the solutions in the saturators. The ammonia andpyridine contents of the gases are absorbed by the solutionsubstantially completely while the gases are passing therethru and, astime goes on, ammonia sulphate precipitates out of the solution andcollects in the bottom parts of the saturators, and the pyridine contentin the solution increases. It is preferable not to begin withdrawal ofthe solution from the saturators until the pyridine content isuficiently high to make the recovery thereof economical. After a fewhours, for example 4 hours, the pyridine concentration in the saturatorsolution will be sufficiently high for this purpose when the enteringgases contain about .15 lb. of pyridine per ton of coal, for at thattime the concentration should be about 1% and thereafter the removal ofthe solution may be continuous. When the pyridine concentrationapproximates 5%, much of the pyridine content in the gases entering thesolution will not be absorbed but will pass out with the outgoing gasesand with the ammonium sulphate. For the most emcient recovery ofpyridine it is, therefore, preferable to maintain the pyridineconcentration under about 1%, altho it may rise to as high as 2% withoutserious losses, and to maintain the acid concentration between about 6%and about 8%. I

When the pyridine in the saturator solution has risen to theconcentration desired, the solution is withdrawn, preferablycontinuously, and the withdrawn solution is treated as it is withdrawn,with ammonia gas in tank H and the pyridine content is recovered in tanki2. The solution which has been freed from pyridine is also preferablycontinuously returned to the saturators. It has been found that when10,000- 12,000 cubic feet of coke oven gas is being treated per minute,and the gas contains about .15 lb. of pyridine bases, the solution maybe continuously withdrawn from the saturator at the rate of about threeto four gallons per minute, and that the recovery under these conditionsis above about 90% of the total pyridine content of the gases. When theloss amounts to as much as 10%, about two-thirds of the loss is by wayof contamination of the sulphate and one-third is by way of the gasleaving the saturators.

When about 3800 tons of coal containing about .15 lb. of pyridine arecoked per day, about 40 to 48 tons of 60 B., commercial sulphuric acidare added per day to the solution in the satura tors to maintain theacid concentration at between about 6% and 7% strength.

The liquid withdrawn from the upper portion of. tank l2 consists ofpyridine, picoline, and higher homologues, together with some solutionof sulphate of ammonia. This liquid may be further treated to recoverand refine these ingredients.

Having thu described the present invention so that those skilled in theart may be able to understand and practice the same, what we desire tosecure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The method of recovering pyridine which includes the steps ofcontinuously passing coke oven gas containing pyridine through a,solution of dilute sulfuric acid in a chamber, maintaining the free acidconcentration of said liquid substantially constant, maintaining thepyridine concentration of said liquid below about 8% continuouslyflowing liquid containing pyridine from a point below the surface ofliquid in said chamber upwardly into and below the surface of the liquidin a second chamber, continuously withdrawing liquid from the secondsaid chamber from a point above the bottom thereof, continuouslytreating the thus withdrawn liquid with ammonia gas to release thepyridine contained therein, continuously separating the thus liberatedpyridine from the liquid by gravity, and continuously returning theliquid from which the pyridine has been so removed to the liquid in thefirst said chamber.

2. The method of recovering pyridine which includes the steps ofcontinuously passing coke oven gas containing pyridine through asolution containing between about 6% and about 8% of sulfuric acid in achamber, maintaining the free acid concentration of said liquidsubstantially constant, maintaining the pyridine concentration of saidliquid below about 2%, continuously fiowing liquid containing pyridinefrom a point below the surface of liquid in said chamber upwardly intoand below the surface of the liquid in a second chamber, continuouslywithdrawing liquid from the second said chamber from a point above thebottom thereof, continuously treating the thus withdrawn liquid withammonia gas to release the pyridine contained therein, continuouslyseparating the thus liberated pyridine from the liquid by gravity, andcontinuously returning the liquid from which the pyridine has been soremoved to the liquid in the first said chamber.

3. The method of recovering pyridine which includes the steps ofcontinuously passing coke oven gas containing pyridine through asolution of dilute sulfuric acid in a. chamber, maintaining the freeacid concentration of said liquid substantially constant, maintainingthe pyridine concentration of said liquid below about 3%, continuouslyflowing liquid containing pyridin from a point below the surface ofliquid in said chamber upwardly into and'below the surface of the liquidin a second chamber, continuously with- V liberated thereby from saidliquid, and continuously returning the liquid to the first said chamber.

. MAX D. WALD.

FRANK A. KARNATZ.

